The fundamental goal of my research program is the elucidation of the mechanisms involved in the coordination and control of DNA replication, chromosome segregation and cell division. Since it is a fundamental attribute of all living cells that there be rigorous coordination of chromosome replication and segregation to insure precise equipartition of the genome at cytokinesis, it seems clear that the study of the mechanisms involved in this coordination is central to our understanding of the regulation of normal and abnormal cell growth. The present proposal is concerned with the continuation of our ongoing program of purification and characterization of the DNA polymerases from the human malignant cell line, KB. We have identified three distinct DNA polymerase activities in KB cells, two of which are associated with the nucleus, and the third with the cytoplasmic fraction. We have expended our major effort to date on rigorous purification and characterization of these activities, and at the present time two of the enzymes appear to be homogeneous. We believe that only by working with homogeneous and rigorously characterized polymerase molecules will it be possible meaningfully to investigate structural and functional interrelationships among them and to begin to explore how the regulation of their biosynthesis and intracellular distribution is related to the coordination and control of DNA synthesis in human cells. Moreover, such studies provide an essential foundation for the understanding of alterations in DNA polymerase structure, function and intracellular distribution that may be associated with virus infection and transformation and with those alterations of normal cell growth regulation that are observed in hyperplastic and neoplastic states.